Apparatus and method for sizing testing

ABSTRACT

A method of measuring a Stockigt sizing degree of a paper or hoard is provided. The method includes: placing a paper or board, to which FeCl 3  (II) is dropped or applied, on NH 4 SCN solution; sequentially capturing, by using a camera, a process of forming reddish brown Fe(SCN) 3  wile the FeCl 3  (II) meets the NH 4 SCN solution penetrating in a thickness direction of the specimen, and recording RGB values of droplet image of the reddish brown Fe(SCN) 3 ; converting the RGB values into HSV values; recording hue (H) value of the HSV values with respect to time; and checking a point where a differentiation value of the H value recorded with respect to time becomes maximum.

TECHNICAL FIELD

The present invention relates generally to a stockigt sizing testing method, and in particular, to a stockigt sizing testing method with reliability and reproducibility, the method including: placing a paper or board, to which FeCl₃ (H) is dropped or applied, on NH₄SCN solution; sequentially capturing, by using a camera, a process of forming reddish brown Fe(SCN)₃ wile the FeCl₃ (II) meets the NH₄SCN solution penetrating in a thickness direction of the specimen, and recording RGB values of droplet image of the reddish brown Fe(SCN)₃; converting the RGB values into HSV values; recording hue (H) value of the HSV values with respect to time; and checking a point where a differentiation value of the H value recorded with respect to time becomes maximum.

BACKGROUND ART

To increase resistance against liquid wetting and penetration, a sizing process is performed on most papers or boards, except tissues and sanitary papers. In such a sizing process, since cellulose containing hydrophilic hydroxyl radical (—OH) is the main component of the paper, a rosin acid sizing agent or neutral sizing agent such as Alkyl Ketene Dimer (AKD) and Alkenyl Succinic Anhydride (ASA) is added to a wet-end system of a paper making process so as to provide water resistance. Examples of a measuring method for evaluating sizing degree of the sized paper include a Cobb testing method, a Hercules testing method, a Stockigt testing method, a Carson curl method, a contact angle measuring method, and a Drop testing method. Among them, the Stockigt testing method is widely used.

According to the Stockigt testing method using liquid penetration, as stipulated in Tappi Useful Method UM-429 and KS M7025, after placing a paper specimen in which a ferric chloride (FeCl₃) is dropped or painted on an ammonium thiocyanate (NH₄SCN) solution, a sizing degree is measured using color development occurring at a time point when the two liquids of NH₄SCN and FeCl₃ are penetrated in a thickness direction (z direction) of the paper to thus form a ferric thiocyanate (Fe(SCN)₃). Color changes in the measurement of the Stockigt sizing degree are illustrated in FIG. 1.

In this method, however, the recognition of the color development time may be different according to each measurer's subjective point of view. Therefore, it is difficult to verify significant difference of the sizing degree with respect to the very highly sized papers.

That is, the Stockigt sizing measuring method is to measure the sizing degree of paper or board by measuring the time point when FeCl₃ and NH₄SCN reacts to cause color development. Since the sizing degree is the time when the reddish brown appears, error according to measurers is great. FIGS. 2 and 3 illustrates changes of Stockigt sizing degree with respect to amount and height of FeCl₃, showing these errors.

Accordingly, in measuring the Stockigt sizing degree for evaluating the water resistance characteristic of the paper, there is demanded a standardized sizing degree measuring method that can overcome the error of measurement results due to obscurity of the measuring method and the measurer's subjective point of view.

DISCLOSURE OF INVENTION Technical Solution

An object of the present invention is to substantially solve at least the above problems and/or disadvantages and to provide at least the advantages below. Accordingly, an object of the present invention is to provide a reliable and objective method of measuring a sizing degree of a paper.

Another object of the present invention is to provide a reliable and objective method of measuring a Stockigt sizing degree.

According to one aspect of the present invention, a method of measuring a sizing degree of a sized paper or board includes: placing a paper or board specimen, to which a first reagent is applied, on a second reagent; sequentially capturing, by using a camera, a process of forming compound taking on a predetermined color wile the first reagent meets the second reagent penetrating in a thickness direction of the specimen, and recording RGB values of droplet image of the compound; converting the RGB values into HSV values; recording hue (H) value of the HSV values with respect to time; and checking a point where a differentiation value of the H value recorded with respect to time becomes maximum.

According to another aspect of the present invention, a method of measuring a Stockigt sizing degree of a sized paper or board includes: placing a paper or board, to which FeCl₃ (II) is dropped or applied, on NH₄SCN solution; sequentially capturing, by using a camera, a process of forming reddish brown Fe(SCN)₃ wile the FeCl₃ (H) meets the NH₄SCN solution penetrating in a thickness direction of the specimen, and recording RGB values of droplet image of the reddish brown Fe(SCN)₃; converting the RGB values into HSV values; recording hue (II) value of the HSV values with respect to time; and checking a point where a differentiation value of the H value recorded with respect to time becomes maximum

DESCRIPTION OF DRAWINGS

FIG. 1 illustrates color change during the measurement of Stockigt sizing degree;

FIG. 2 illustrates a change of the Stockigt sizing degree with respect to dropping height of FeCl₃;

FIG. 3 illustrates a change of the Stockigt sizing degree with respect to dropping volume of FeCl₃;

FIG. 4 illustrates sequential still images obtained during the Stockigt test according to measurement time;

FIG. 5 illustrates a segmentation processing of extracting only a droplet shape of FeCl₃ solution, except a background image;

FIG. 6 illustrates a change of HSV during the measurement of Stockigt sizing degree;

FIG. 7 illustrates a change of H with respect to time during the measurement of Stockigt sizing degree;

FIG. 8 illustrates a differential change of H with respect to time during the measurement of Stockigt sizing degree;

FIG. 9 illustrates mask used to calculate a differential change of H with respect to during the measurement of the Stockigt sizing degree;

FIG. 10 illustrates a Stockigt sizing testing apparatus according to the present invention; and

FIG. 11 illustrates the comparison of Stockigt sizing measurement results according to the related art and the present invention.

BEST MODE

Preferred embodiments of the present invention will be described herein below with reference to the accompanying drawings. In the following description, well-known functions or constructions are not described in detail since they would obscure the invention in unnecessary detail.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

Paper used in this invention is a paper of 70 g/m² made by an experimental Tappi standard sheet machine, based on Tappi T 205, using a paper material beat up to 400 mL CSF through an experimental Valley beater using Canadian Radiata pine ECF coniferous bleached kraft pulp.

Alkyl Ketene Dimer (AKD) used in the paper sizing process added 0, 0.2, 0.4, 0.6, 0.8, and 1% with respect to ovendry weight of the paper. To dispersion and fixing of the AKD, 0.3% cationic starch with respect to the ovendry weight of pulp was added. Before the beat paper material, AKD, and the cationic starch were placed into the Tappi standard sheet machine, they were agitated at 800 rpm for 30 seconds using the experimental disperser.

Reagent used in the Stockigt sizing degree test used 7% ferric chloride (FeCl₃) (II) solution and 6% ammonium thiocyante (NH SCN) solution according to the regulation digital video camcorder and CMOS digital camera were used.

The Stockigt sizing degree testing method includes a method of TAPPI Useful Method UM 429 and a method of KS M 7025. In the TAPPI Useful Method UM 429, FeCl₃ is applied thinly on a test specimen, and NH₄SCN solution is dropped on the specimen. A time is measured until perfect reddish brown appears on the solution to which FeCl₃ is applied, and the measured time is represented as the sizing degree. On the contrary, in the KS M 7025, 2% FeCl₃ (II) solution is dropped on a paper specimen, and the specimen is placed on 1% NH₄SCN solution. A time is measured until three or more reddish brown spots appear on the FeCl₃ (II) solution, and the measured time is represented as the sizing degree.

This invention used the method of TAPPI Useful Method UM 429 and recorded the time when perfect reddish brown appears as an ending point of the sizing degree measurement.

To provide reliability and reproducibility of the Stockigt test results, algorithm for determining color development time is constructed using sequential image input, division, and color conversion functions so as to automatically perceive the color de-velopment time while minimizing all error that may occur during the sizing degree measurement.

Since the Stockigt sizing degree test method measures the time when the color of FeCl₃ dropped into the paper specimen is changed into perfect reddish brown, color changes of droplet according to time is required to be sequentially recorded in order for a computer to automatically recognize the color change during the measurement. Therefore, the automatic image acquisition developed in this study is obtained according to time, and these obtained images are called sequential image. As illustrated in FIG. 4, sequential images obtained during the Stockigt test are sequence of still images according to measurement time, appearing 3-D shape. FIG. 4 illustrates still images obtained according to measurement time during the Stockigt test.

To trace only color change during the Stockigt test, only shape of FeCl₃ at T_(i) must be extracted among the sequential images. The only shape of the droplet, except background image, is extracted so as to obtain accurate color value of the solution varying with time. This operation is called a segmentation processing. FIG. 5 illustrates the segmentation processing to extract only the shape of droplet of FeCl₃, except background image.

The segmented image means an image of only droplet, except the background image, as illustrated in FIG. 5. For this segmentation, a color binarization widely used in an image analysis is used.

To quantify color changes of droplet from the sequential images, only color must be detected from the respective images. To find the color change of FeCl₃ from initial color to reddish color, it can be assumed that hue among color components is important. By quantifying the hue value, the color development time was found. However, each pixel value obtained from the droplet image outputted from a computer is expressed as a combination of red (R), green (B), and blue (B), not the hue values. These RGB values are significantly different from human color perception. Therefore, these RGB values are required to convert into hue (H), saturation (S), and value (V).

Using HSV model, color can be divided into hue, saturation, and value. Therefore, each color components can be observed in linear terms.

Although there are several methods of converting RGB into HSV, a following method is widely used. When an input value is converted into HSV, RGB values are first converted into YC₁C² values using Eq. 1 below.

$\begin{matrix} {\begin{bmatrix} Y \\ C_{1} \\ C_{2} \end{bmatrix} = \begin{bmatrix} \frac{1}{3} & \frac{1}{3} & \frac{1}{3} \\ 1 & {- \frac{1}{2}} & {- \frac{1}{2}} \\ 0 & {- \frac{\sqrt{3}}{2}} & \frac{\sqrt{3}}{2} \end{bmatrix}} & (1) \end{matrix}$

YC₁C₂ values are converted into HSV coordinate system using Eq. 2 below.

V=Y

S=√{square root over (C ₁ ² −C ₂ ²)}

If C₂≦0, then H=cos

Else H=2π−cos  (2)

Value (V) represents a mean black and white gray scale, Hue (H) represents color that is not influenced by shadow due to optical point, and Saturation (S) represents fineness of hue. The HSV values are normalized in a range of 0 to 255.

A method of calculating a specific vector of a color and a method of determining a color development time are proposed. To determine the time when the color is changed, characteristic vector of hue among the division regions of the sequential images is calculated.

H={η₁, η₂, η₃, . . . , η_(i), . . . , η_(N)}

η_(i) =∥h _(i)∥  (3)

where i: time of sequential image, N: number of entire acquired images, H: set of characteristic vectors of sequential image, η_(i): i^(th) characteristic vector, h_(i): colors con-stituting i^(th) image.

In Eq. (3), the set of characteristic vectors are expressed. This model expresses changes of liquid color within the sequential images. Each component of H means an average value of hue.

FIG. 6 illustrates change of HSV during the measurement of Stockigt sizing degree. As illustrated in FIG. 6, the set expressed as a graph can be considered as changes of hue values, that is, characteristic vectors with respect to time.

FIG. 7 illustrates changes of H with respect to time during the measurement of Stockigt sizing degree. In FIG. 7, time t is a color development time when reddish brown appears.

Among several methods, a differentiation method was used. FIG. 8 illustrates dif-ferentiation changes of H with respect to time during the measurement of Stockigt sizing degree. This differentiation method can be expressed as Eq. (4) below.

$\begin{matrix} {{\nabla H} = \frac{\partial H}{\partial x}} & (4) \end{matrix}$

To apply to a discrete value, a mask of FIG. 9 was actually used. That is, FIG. 9 illustrates a mask used to calculate differentiation change of H with respect to time during the measurement of Stockigt sizing degree.

The differentiation is locally performed using the mask of FIG. 9(A) like in Eq. (5) below.

∇f≈|z ₁ −z ₂|  (5)

In Eq. (5), the differentiation value of the interest point z₂ is similar to difference between adjacent points z₁ and z₃, and a value of each mask is illustrated in FIG. 9(B). This mask is sequentially applied to a function f. This method is called a convolution.

FIG. 10 illustrates an apparatus for measuring the Stockigt sizing degree according to the present invention. The apparatus includes an automatic liquid dispenser for applying a first reagent on a paper or board specimen, and a specimen shifter for placing the paper or board specimen on a second reagent. Also, an image capturing device sequentially captures a process of forming a compound of a predetermined color while the first reagent and the second reagent penetrating in a thickness direction of specimen are encountered, and records RGB values of droplet images of the compounds. A computer with software converts the RGB values captured by the image capturing device into HSV values, records changes of H with respect to time, and checks a point where a differentiation value with respect to time is changed to the maximum.

FIG. 11 illustrates the measurement results of Stockigt sizing degree according to the related art and the present invention. As illustrated in FIG. 11, 0.4% or more of AKD is added to the sheet and thus the sizing degree measured by the related art is higher than that measured by the automatic measuring method. Also, error angle of the sizing degree measured according to addition level of the AKD exhibits higher change than that measured by the automatic measuring method of the present invention. On the contrary, the sizing degree measured by the automatic measuring method of the present invention is similar to the values measured by the related art while increasing the addition of AKD. However, it can be easily checked that error range is much smaller. According to the conventional measurement, an ending point where reddish brown appears is read, based on the measurer's subjective point of view. Therefore, error range is large with respect to the same specimens. Therefore, the present invention can obtain the reproducible results.

According to the present invention, the method of measuring a Stockigt sizing degree of a sized paper or board includes: placing a paper or board, to which FeCl₃ (II) is dropped or applied, on NH₄SCN solution; sequentially capturing, by using a camera, a process of forming reddish brown Fe(SCN)₃ wile the FeCl₃ (II) meets the NH₄SCN solution penetrating in a thickness direction of the specimen, and recording RGB values of droplet image of the reddish brown Fe(SCN)₃; converting the RGB values into HSV values; recording hue (H) value of the HSV values with respect to time; and checking a point where a differentiation value of the H value recorded with respect to time becomes maximum.

While the invention has been shown and described with reference to certain preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. 

1. A method of measuring a sizing degree of a sized paper or board, comprising: placing a paper or board specimen, to which a first reagent is applied, on a second reagent; sequentially capturing, by using a camera, a process of forming compound taking on a predetermined color wile the first reagent meets the second reagent penetrating in a thickness direction of the specimen, and recording RGB values of droplet image of the compound; converting the RGB values into HSV values; recording hue (H) value of the HSV values with respect to time; and measuring the sizing degree by checking a point where a differentiation value of the H value recorded with respect to time becomes maximum.
 2. The method of claim 1, wherein the first reagent is FeCl₃ (II), the second reagent is NH₄SCN solution, and the compound is reddish brown Fe(SCN)₃.
 3. The method of claim 1, wherein the recording of the RGB values of the droplet image of the compound comprises: obtaining sequential images showing color changes of the droplet of the compound with respect to time; removing background image from the sequential images obtained a segmentation processing using a color binarization method; and extracting only shape of droplet.
 4. A method of measuring a Stockigt sizing degree of a sized paper or board, comprising: placing a paper or board, to which FeCl₃ (II) is dropped or applied, on NH₄SCN solution; sequentially capturing, by using a camera, a process of forming reddish brown Fe(SCN)₃ wile the FeCl₃ (II) meets the NH₃SCN solution penetrating in a thickness direction of the specimen, and recording RGB values of droplet image of the reddish brown Fe(SCN)₃; converting the RGB values into HSV values; recording hue (H) value of the HSV values with respect to time; and measuring the sizing degree by checking a point where a differentiation value of the H value recorded with respect to time becomes maximum.
 5. An apparatus for measuring a sizing degree of a sized paper or board, comprising: a unit for applying a first reagent on a paper or board specimen; a unit for playing the paper or board specimen on a second reagent solution; an image capturing unit for sequentially capturing a process of forming compound taking on a predetermined color wile the first reagent meets the second reagent penetrating in a thickness direction of the specimen, and recording RGB values of droplet image of the compound; a unit for converting the RGB values into HSV values; and a unit for recording hue (H) value of the HSV values with respect to time, and measuring the sizing degree by checking a point where a differentiation value of the H value recorded with respect to time becomes maximum.
 6. The apparatus of claim 5, wherein the image capturing device obtains sequential images showing color changes of the droplet of the compound with respect to time, removes background image from the sequential images obtained a segmentation processing using a color binarization method, and extracts only shape of droplet. 